Wire coating composition



Patented Aug. 24, 1954 WIRE COATING COMPOSITION Emil H. Olson, Muskegon, Mich., assignor to Anaconda Wire and Cable Company, a corporation of Delaware No Drawing. Application December 29, 1951, Serial No. 264,223

7 Claims. 1

This invention relates to an improved wire coating composition for use in making insulated magnet wire of the enameled magnet wire type. The invention further contemplates the provision of an improved magnet wire made by applying to a metallic conductor a thin film of the new coating composition. This invention is a continuatiominpart of my application Serial No. 76,661, filed February 15, 1949, now Patent No. 2,570,476, dated October 9, 1951.

In my aforesaid patent, I have described and claimed a wire coating composition that sets by gelation, consisting essentially of a cellulose ester of one or more aliphatic acids containing from 2 to 4 carbon atoms, dissolved in a solvent composed essentially of 15% to 30% of a lower monohydroxy alkanol, 50% to 60% of benzene or one or more of its methyl homologues, and to 30% of a lower dialkyl ketone. The amount of ester employed in this coating composition in relation to the amount of solvent is sufiicient to impart to the composition a viscosity in the range of 600 to 1500 centipoises at a temperature of 100 F., but in any event is not less than about 12% by weight of the composition. It is characteristic of the composition that it sets to a non-flowing solid by gelation upon being cooled to room temperature, say, about 65 F., without solvent evaporation being necessary for such solidification to occur.

The aforesaid coating composition has the advantage that a single coat applied to a wire, in an operation involving drawing the wire through a bath of the composition at a temperature above its gelation temperature, suffices to form on the wire a coating of adequate thickness to meet the dielectric requirements of wire coating compositions as generally applied to magnet wires; and furthermore, the prolonged baking operation that is a necessary part of making conventional enameled magnet wires is eliminated. Wires may be coated with the gelable coating composition at much higher rates of wire travel through the coating bath than is possible with conventional wire enamels. However, a disadvantage of the coating composition of my aforesaid application is that for some purposes its resistance to abrasion is undesirably low. For this reason, wires coated with the composition of my aforesaid patent have not found man opportunities for use in structures where abrasion resistance of the wire coating is of marked importance, as, for example, in motor coils where the coils must be forced into slots in which they fit tightly.

I have discovered that the abrasion resistance of insulating coatings formed on magnet wire by gelable lacquer coating compositions of the character described in my aforementioned patent can be very much increased by incorporating in the lacquer composition a minor proportion of tageously about 10% by weight of a drying-oil modified resinous condensation polymer of a polyhydric alcohol and a substance selected from the group consisting of polybasic acids and their anhydrides (e. g. phthalic anhydride), the oil content of said oil-modified polymer being in the range from 30% to 50% by weight thereof, said solute being dissolved in asolvent composed cssentially of approximately one part by weight of a lower monohydroxy alkanol, 3 parts by weight of a substance selected from the group consisting of benzene and its methyl homologues, and 1 part by weight of a lower dialkyl ketone (however, thoroughly satisfactory coating compositions may be made in which the proportions of the solvent constituents differ substantially from those given). The proportions of solute to solvent in the coating composition are such as to yield a lacquer which is fluid at temperatures above, say 100 F., but which gels to a non-flowing solid at or near room temperature, say at about F. For best results the proportion of solute to solvent is in the range from 1:10 to 1: 1. e. the. solute constitutes from 10% to 17% by weight of the composition; and in any event the amount of solute used is sufiicient to impart to the composition a viscosity at F. in the range from. 600 to 1500 centipoises. Generally it is desirable, but it is not essential, to incorporate in the lacquer composition one or more chemically inert. pigments or opaquing. agents, which ingredients may be employed in the proportions of about 3% to 10% by weight of the solute composition. Other ingredients which do not essentially alter the character of the coating composition also may be added as desired.

It is apparent that the coating composition of this invention is generally the same as that described in my aforementioned Patent No. 2,570,476, but with the replacement of a portion of the cellulose ester with a corresponding amount of the drying-oil-modified alkyd resin. The solvent composition is indeed that of my said patent, and here, as in that patent, I use a lower monohydroxy alkanol boiling at a tem-;

perature of about 100 C. or less at atmospheric pressure. I may, of course, also use low boiling commercial alcohol base solvents such as the one composed of about 92% commercial ethyl alcohol, about 4.8% methyl alcohol, about 1.4% methyl isobutyl ketone, about 1% ethyl acetate, and about 1% hexane mentioned in. my aforetioned patent. The particular solvent material as noted above and as set forth in the claims is of course broad enough to include such monohydroxy alkanol base solvents such as the commercial solvent above noted. Similarly, I use a lower dialkyl ketone having from 3 to 6 carbon atoms and boiling at a temperature of about 100 C. or less at atmospheric pressure.

The cellulose esters that are used in the new lacquer composition are the same that have been used heretofore in dip coating lacquers and in the wire coating composition of my aforementioned patent, and include cellulose acetate, cellulose propionate, cellulose butyrate, and mixed esters such as cellulose acetate propionate containing, say, to acetyl and to propionyl, and cellulose acetate butyrate containing, say, 12% to 18% acetyl and 15% to butyryl.

The alkyd resin characteristically employed in the coating composition of the present invention is of the type known to the trade as a short oil oxidizing alkyd resin, and constitutes a dryingoil-modified resinous condensation polymer of a polybasic acid or acid anhydride and a polyhydric alcohol in which the oil content is in the range from 30% to 50% by weight. Typically it is prepared by reacting the polybasic acid or acid anhydride, such as phthalic, maleic, fumaric or carbic acid or anhydride with glycerol, a glycol, pentaerythritol, or other polyhydric alcohol and with the drying oil (e. g. linseed oil, dehydrated castor oil, soy-bean oil, China wood oil, oiticica oil, or a fish oil) in the presence of a catalyst. Perhaps the most satisfactory of these resins is the glyceryl phthalate polymer prepared by reaction of phthalic anhydride with glycerol and soy bean or equivalent drying oil. The alkyd resin is most advantageously incorporated in the lacquer composition in the form of a solution containing, say, 50% to 85% by weight of the alkyd resin constituent and the balance solvents such as xylol, toluol, or mineral spirits. In gen eral I prefer to employ the solutions of these oilmodified condensation polymers which are commercially available. In making up the composition from such solutions, the amount of the non-volatile polymer constituent therein is alone taken into account in determining the solute proportions of the composition, and the volatile solvent constituents of the polymer solution are taken into account as components of the solvent of the lacquer composition.

Following is an example of a typical wire coating composition prepared in accordance with this invention:

Coating compositions prepared in accordance with the invention are most advantageously applied to wires by the method described and claimed in United States Patent No. 2,547,047 to Harry L. Saums, John H. Vail and Howard W. Sturgis, using apparatus of the character described and claimed in United States Patent No. 2,558,993 to Howard. W. Sturgis and Emil I-I. Olson. Briefly, the method of applying the coating composition to the wire involves passing the wire into a bath of the composition maintained at a temperature well above its gelation temperature, and then withdrawing the wire with a film of the coating composition adhering thereto. This film cools almost at once as the wire emerges into the room atmosphere to below its gelation temperature and thereby sets almost immediately to a non-flowing solid film. Eventually the volatile constituents of the gelled film evaporate and of course the oil-modified resin composition oxidizes, leaving a wire coated with an intimate blend of the non-volatile constituents of the lacquer. The finished wire thus comprises a metallic conductor having thereon a thin substantially uniform and continuous coating composed essentially of 80% to 95% by weight of a cellulose ester of at least one aliphatic acid containing from 2 to 4 carbon atoms (e. g., cellulose acetate butyrate), intimately blended with 5% to 20% by weight of an oxidized drying-oil-modified resinous condensation polymer of a polybasic acid (or anhydride) and a polyhydric alcohol.

It is a major advantage of coating compositions prepared in accordance with the invention that the insulating film formed by its use on the surface of the wire is substantially continuous with but very few and widely separated pinholes even when the coating is applied at a high rate of wire speed. Also, the coating is uniform in thickness about the periphery of the Wire and along its length, and, most important, it is tightly adherent to the wire and highly resistant to abrasion.

The remarkably improved characteristics of wire coated with the composition of this invention, in comparison with a wire coated with a gelable lacquer prepared in accordance with my aforementioned patent, is illustrated by the test results summarized in Table I; In each of the tests mentioned, the wire designated as wire A was prepared in accordance with this invention by coating a bare No. 36 A. W. G. copper conductor with the particular coating composition given by way of example above; and the wire designated as wire B was made by applying to a bare No. 36 A. W. G. copper conductor a coating composition identical in all respects with that Parts by of the above example, save only that the drying- Ingredlent Weight oil-modified oxidizing alkyd resin was omitted and a corresponding increase was made in the gelluloscg iceta g bg yre te 5 1i 2 amount of cellulose acetate butyrate employed Tying-Oi 4110 l e 0X1 lZ nga r8511). Ferric oxide (pigment) l. 3 1.2 In the compasltlon- Titanium dioxide (opaquing agent). 0.7 0. 7 I Mixed lower monohydroxy alkanols (mostly Table ethyl alcohol) 18.0 17. l. Toluol 54.8 2.3 Acetone 18.0 17.1 Wire A Wire 3 In this composition, the solids constitute 14.2 Serene Test (Wire asedl Week) 9 v Continuity Test 1 1. 3 I- 3 pa ts y w ht 01 3 y w t of t Abrasion Test (wireaged 1 day) 14s 40 position, and the solvent components constitute Abraswn t (wire agedlmonth) 2306 333 90.8 parts by weight or 86.5% by weight of the composition. This composition has a viscosity of about 1000 to 1200 centipoises at 100 F. and solidifies by gelation when cooled to a temperature of about 65 F.

1 Figures given for these tests are averages of three separate determinations.

' Scrape test.-The so-called Delco scrape test was used in obtaining the data given in the table. In this test the wire is pulled horizontally under the point of a needle, the needle being mounted so that it bears on the wire with a weight that can be varied. The needle and the wire are connected together in a low-voltage electrical circuit. The weight (in ounces) on the needle which is just sufficient to cause the needle to scrape through the coating on the wire and complete the electric circuit is taken as an index of the scrape resistance of the wire. The great-er the weight with which the needle must be loaded, the better is the quality of the coating insofar as regards its scrape resistance.

Continuity test-To determine the continuity of a coating film on a wire, the coated wire is drawn through a pool of mercury. The wire and the mercury are connected together in an electric circuit which is completed whenever the mercury comes in direct contact with the metal of the wire through a perforation or discontinuity in the coating. The number of times the circuit is thus completed per hundred feet of wire drawn through the mercury pool is taken as an index of film continuity. The smaller the number of such circuit completion, the better is the quality of the wire.

Abrasion test-The abrasion resistance of the coating compositions as given in the above table was determined by the use of an apparatus comprising twelve hard cylindrical spokes, each onequarter inch in diameter and arranged in the form of a cylindical cage mounted for rotation about a horizontal axis. The wire to be tested is anchored at one end, and the other end is passed over the spokes, being held down against the spokes by a weight attached to its other end. The metallic conductor of the wire and the spokes of the cage are connected together in an electrical circuit and the cage is rotated so that each spoke rubs along the coating on the wire with each revolution of the cage. When the spokes have worn through the coating and make contact with the metallic conductor, an electrical circuit which stops the apparatus is completed. The number of revolutions which the cage makes until such circuit is completed is an index of the resistance of the wire to abrasion.

The greater the number of rotations which the cage makes before the circuit is completed, the greater is the abrasion resistance of the coating.

It will be noted from Table I above that wire A, made in accordance with the present invention, was greatly superior in scrape resistance and in abrasion resistance to wire 13, prepared using the best gelable lacquer wire coating composition heretofore known. With respect to abrasion resistance, the relative superiority of the wire of this invention increased markedly as the wire aged, as evidenced by the fact'that its abrasion resistance index was between three and four times greater than that of the comparative wire at the age of one day (Abrasion test A), but 7 was about seven times greater at the age of one month (Abrasion test B.) Even in the continuity test, the wire of this invention showed marked improvement over the wire made with plain gelable lacquer. These outstanding test results are indicative of the much wider range of usefulness under conditions imposing substantial abuse on the insulating coating, of wire made in accordance with this invention as compared With wire made with the unmodified gela- 6. ble lacquers of my aforesaid Patent No. 2,570,476.

I claim:

-1. A wire coating composition consisting essentially of a solute composed essentially of (a) 80% to 95% by weight of cellulose acetate butyrate and (b) 5% to 20% by weight of a drying-oilmodified oxidizing alkyd resin in which the oil content is in the range from 30% to said solute being dissolved in a solvent composed essentially of approximately 1 part by weight of a lower monohydroxy alkanol containing 1-5 carbon atoms and having a boiling point of about 100 (2., 3 parts by Weight of a substance selected from the group consisting of benzene and its methyl homologues, and 1 part by weight of a lower dialkyl ketone containing 36 carbon atoms and having a boiling point of about 100 0., said composition having a viscosity in the range from 600 to 1500 centipoises at 100 F. and gelling to a non-flowing solid at about F.

2. A wire coating composition consisting essentially of a solute composed essentially of (a) to by weight of a cellulose ester of at least one aliphatic acid containing from 2 to 4 carbon atoms and (b) 5% to 20% by weight of a drying-oil-modified resinous condensation polymer of a polyhydric alcohol and a substance selected from the group consisting of polybasic acids and their anhydrides, the oil content of said oil-modified polymer being in the range from 30% to 50% by weight thereof, said solute being dissolved in a solvent composed essentially of approximately 1 part by weight of a lower monohydroxy alkanol containing 1-5 carbon atoms and having a boiling point of about C. 3 parts by weight of a substance selected from the group consisting of benzene and its methyl homol-ogues, and 1 part by weight of a lower dialkyl ketone containing 3-6 carbon atoms and having a boiling point of about 100 C., said composition having a viscosity in the range from 600 to 1500 centipoises at 100 F. and gelling to a non-flowing solid at about 65 F.

3. A wire coating composition consisting essentially of a solute composed essentially of (a) 80% to 95% by weight of a cellulose ester of at least one aliphatic acid containing from 2 to 4 carbon atoms and (b) 5% to 20% by weight of a dryingoil-modified resinous condensation polymer of phthalic anhydride and a polyhydric alcohol, the oil content of said oil-modified polymer being in the range from 30% to 50% by weight thereof, said solvent being dissolved in a solvent composed essentially of approximately 1 part by weight of a lower monohydroxy alkanol containing 1-5 carbon atoms and having a boiling point of about 100 C., 3 parts by weight of a substance selected from the group consisting of benzene and its methyl homologues, and 1 part by weight of a lower dialkyl ketone containing 3-6 carbon atoms and having a boiling point of about 100 0., said composition having a viscosity in the range from 600 to 1500 centipoises at 100 F. and gelling to a non-flowing solid at about 65 F.

4. A wire coating composition consisting essentially of a solute composed essentially of about 90% by weight of cellulose acetate butyrate and about 10% by weight of a drying-oil-modified resinous condensation polymer of phthalic anhydride and a polyhydric alcohol, the oil content of said oil-modified polymer being in the range from 30% to 50% by weight thereof, said solvent .being dissolved in a solvent composed essentially of approximately 1 part by weight of a lower monohydroxy alkanol containing 1-5 carbon atoms and having a boiling point of about 100 C.,

,3 parts by weight of a substance selected from the group consisting of benzene and its methyl homologues, and 1 part by weight of a lower dialkyl ketone containing 3-6 carbon atoms and having a boiling point of about 100 0., said composition having a viscosity in the range from 600 to 1500 centipoises at 100 F. and gelling to a non-flowing solid at about 65 F.

5. Magnet wire comprising a metallic conductor having thereon a thin substantially uniform and continuous coating composed essentially of 80% to 95% by weight of a cellulose ester of at least one aliphatic acid containing from 2 to 4 carbon atoms intimately blended with 5 to 20% by weight of an oxidized drying-oil-modified resinous condensation polymer of a polybasic acid and a polyhydric alcohol, the drying oil content of said oil-modified polymer being in the range from 30% to 50% by weight thereof.

6. Magnet wire comprising a metallic conductor having thereon a thin substantially uniform and continuous coating composed of an intimate 8 blend of approximately 80% to 95% by weight of cellulose acetate butyrate, with 5% to 20% by weight of an oxidized drying-oil-modified alkyd resin, the drying oil content of said oil-modifiedpolymer being in the range from to by weight thereof.

'7. Magnet wire comprising a metallic conductor having thereon a thin substantially uniform and continuous coating composed of about by weight of cellulose acetate butyrate intimately blended with about 10% by weight of an oxidized drying-oil-modified resinous condensation polymer of phthalic anhydride with a polyhydric alcohol, the drying oil content of said oil-modified polymer being in the range from 30% to 50% by weight thereof.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,925,903 Hovey Sept. 5, 1933 2,084,825 Ruben June 22, 1937 2,186,454 Gloor Jan. 9, 1940 

1. A WIRE COATING COMPOSITION CONSISTING ESSENTIALLY OF A SOLUTE COMPOSED ESSENTIALLY OF (A) 80% TO 65% BY WEIGHT OF CELLULOSE ACETATE BUTYRATE AND (B) 5% TO 20% BY WEIGHT OF A DRYING-OILMODIFIED OXIDIZING ALKYD RESIN IN WHICH THE OIL CONTENT IS IN THE RANGE FROM 30% TO 50%, SAID SOLUTE BEING DISSOLVED IN A SOLVENT COMPOSED ESSENTIALLY OF APPROXIMATELY 1 PART BY WEIGHT OF A LOWER MONOHYDROXY ALKANOL CONTAINING 1-5 CARBON ATOMS AND HAVING A BOILING POINT OF ABOUT 100* C., 3 PARTS BY WEIGHT OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF BENZENE AND ITS METHYL HOMOLOGUES, AND 1 PART BY WEIGHT OF A LOWER DIALKYL KETONE CONTAINING 3-6 CARBON ATOMS AND HAVING A BOILING POINT OF ABOUT 100* C., SAID COMPOSITION HAVING A VISCOSITY IN THE RANGE FROM 600 TO 1500 CENTIPOISES AT 100* F. AND GELLING TO A NON-FLOWING SOLID AT ABOUT 65* F. 